The invention relates to automatic assembly apparatus for locating a first component present at a first initial position for assembly with a second component present at a second initial position, said assembly taking place at an assembly position, said apparatus comprising parallel projection means for imaging said first and second components when positioned in respective relative orientations with respect to said respective initial positions, said parallel projection means comprising in order away from the respective component a field lens, an objective lens positioned at the principal focal plane of the field lens, and an electronic camera for receiving a real image of the component formed by the objective lens and for producing a spatially quantized picture signal, said apparatus comprising gripper control means for controlling a gripper to move a component, initially remote from the assembly position, towards the assembly position, said apparatus having futhermore data processing means for receiving said picture signal and for measuring and storing any initial position remote from the assembly position and therefrom calculating movement commands for said gripper control means. Such a system has been published in the article "The application of parallel projections to three-dimensional object location in industrial assembly", by B. M. Jones and P. Saraga, Pattern recognition, Vol. 14 (1981) pp. 163-171. The optical system has in particular been disclosed in U.K. patent application No. 2.065.299A to Applicant, corresponding U.S. patent application Ser. No. 211.554 herein incorporated by reference. The assembly position may be either at the first initial position or at the second initial position, or remote from both initial positions. The second initial position may be also determined by means of the optical system, but alternatively may be known by other means. If the assembly position is remote from both initial positions it may also be determined by means of the optical system, but alternatively may be known by other means. The gripper position may be calibrated by means of the optical system, but alternatively may be known by other means. The gripper motion may also be measured by means of the optical system for generating a feedback quantity, but alternatively this motion may be known by other means. Such other means could be either a rigid structure having invariable dimensions, or intermittent calibration by an operator, or other measuring means such as microwave detectors. The initial positions themselves could be static. Alternatively, one or both of them could be moving, e.g. in that a component is transported on a conveyor belt at uniform speed.
In such vision controlled automatic assembly apparatus it has been the practice to control the appearance of the components to be assembled and/or the lighting conditions so that simple black/white pictres are available. These pictures can be converted relatively easily to binarized pictures by applying a relatively poorly defined threshold level to a video signal provided by the electronic camera which receives an image of the components. The advantage of using parallel optical rays for imaging the component is that the dimensions of the component as represented in the picture signal are independent of the position of the component. It has been found that this allows for greater correctness in determining the component feature positions and threshold levels to be used her inafter. Notably the absence of parallax phenomena will cause the projected dimensions always to be equal to the real dimensions, so that only the limited deviations caused by the optical system itself may cause uncertainties (such as Airy-discs and the elementary diffraction effects caused by their superposition). Note that spatial quantization is conventionally executed according to a regular matrix of pixels. It should also be noted that the parallel projection means may consist of one system for locating both components. This may be feasible in the case of small components, or when the optical system itself can be moved in a calibrated way, for example, if it is mounted on the gripper. Alternatively, there are more parallel projecting systems, one for each component, or even more than one parallel projecting system for one component. The gripper may also be located while it is positioned in the field of any parallel projecting system either for calibration, or, when it is continually monitored while at the assembly position, for purposes of feedback in order to realize still greater accuracy and/or increased speed of assembling.
The expected dimensions of the components can be predetermined and stored in a digital computer. The computer can then be programmed to operate on the binarized information and the stored information identify each component and measure its position and orientation in the binarized picture and hence in the assembly area.
In practical situations it would be an advantage if normal grey-level pictures from the camera could be used. Predetermined features on the component could then be used to identify, position and orientate the component. However if a single threshold level is applied to the video waveform of a grey-level picture, some wanted features are lost and/or unwanted or irrelevant detail appear in the binarized picture.